It is old to equip a rigid front axle for industrial forklift trucks with just a single hydraulic motor. The hydraulic motor in such cases is fitted on the outside of the front axle in the region between the respective axle-centering flanges, the hydraulic motor being a high-speed hydraulic motor. The axis of rotation of the high-speed hydraulic motor is thus arranged axially parallel to the longitudinal axis of the front axle. Such an axle does not meet the requirements for high compactness, since the hydraulic motor externally flange-mounted on it requires not only additional transmission elements, (e.g., transmission gear mechanisms, from the hydraulic motor to the respective axle stubs) but also a relatively large installation space.
Also known are axle assemblies into which two hydraulic motors are integrated to power a driven wheel. Although such axle assemblies with two integrated hydraulic motors have greater compactness than axle assemblies with an externally mounted high-speed hydraulic motor with respect to the outer dimensions, the twin hydraulic motors to be provided make these axle assemblies relatively expensive and therefore also complicated in their construction.
DE 43 11 997 A1 describes a hydraulic motor which is provided with a hollow shaft. This known hydraulic unit has reduced system-dependent axial force components and, as a unit, is provided with a mounting which takes up little installation space. Such a low-speed radial-piston motor typically has speeds of up to 300 rpm and delivers adequate torque for a wheel drive of a mobile vehicle, without a further transmission being required, if each wheel has its own drive. Neither a differential nor its arrangement inside an axial assembly are described.
DE 33 07 047 A1 describes a unit which comprises an axial-piston motor and epicyclic gearing in the form of a bevel-gear differential mechanism, the differential mechanism being arranged inside the axial-piston motor, which is of the swash-plate type of design. A spatially favorable arrangement and undemanding requirements for installation space are achieved by arranging a differential directly inside an axial-piston motor. In comparison with the radial-piston motors, the radial dimensions of the axial-piston motors are much smaller. This makes it possible to provide a unit which meets the requirement for a small installation space, in which unit the differential is surrounded directly and completely by an axial-piston motor. Also described is the use of a radial-piston motor and provision of the differential inside it. However, this leads to very large dimensions of the axle assembly and consequently not a compact construction. The arrangement of a differential within the motor of the known unit together with the endeavor to achieve a compact construction have the result, however, that the differential cannot transfer in the given space the torque which is to be transferred.
Consequently two possibilities for designing the axle assembly of a mobile work vehicle are known in the prior art. According to the first possibility, the drive motor is arranged outside the longitudinal axis of the axle assembly, it being possible for the differential to be integrated in the axle assembly. The disadvantage of such an arrangement is a relatively large radial dimension, which is at odds with the requirement for high compactness. The second possibility for the drive is to arrange the motor within the axle and to integrate the differential in the motor, i.e. the drive motor completely surrounds the differential. The disadvantage is, on the one hand, that for large torque to be transferred by the differential likewise large radial dimensions are required and, on the other hand, with smaller radial dimensions large required torque cannot be transferred.
The invention is therefore based on the object of providing a mobile work vehicle with a minimized number of hydraulic-motor drives with high torque transmission, the driven axle assemblies of which have a compact construction. The advantages of low-speed radial-piston motors is that they do not require any mechanical transmission, but nevertheless permit the vehicle to travel around bends without the drive wheels slipping.
These and other objects of the invention will be apparent to those skilled in the art.